Mounting structure for capacitors

ABSTRACT

The mounting structure has a plurality of unit capacitors ( 1 ) comprising ceramic capacitor elements ( 2 ) with terminals ( 3 ), ( 4 ), and a three-tier substrate ( 10 ) comprising an insulating layer ( 11 ) sandwiched between two electrodes ( 12 ), ( 13 ). A plurality of apertures ( 15 ) is formed in the first electrode, in which are positioned bosses ( 16 ) being continuous with the second electrode ( 13 ), while the plurality of unit capacitors ( 1 ) is arranged on the first electrode ( 12 ), one terminal of each unit capacitor ( 1 ) being in contact with the first electrode ( 12 ) and the other with the second electrode ( 13 ) via a boss ( 16 ) so as to connect all the unit capacitors ( 1 ) electrically in parallel fashion. 
     In this manner a mounting structure for capacitors is provided which permits of high capacity in a compact form.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to Japanese Application No.JP2000-282196 filed on Sep. 18, 2000, the entire content of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mounting structure for capacitorslocated, for instance, on a circuit comprising a power semiconductordevice.

2. Description of the Related Art

Generally speaking, where a power semiconductor device is used as aswitching device, the semiconductor device is provided with a snubbercircuit or smoothing circuit including a capacitor.

In the case of a snubber circuit, the collector and emitter of thesemiconductor device are provided with a series circuit with capacitorand diode to absorb surge voltage of the semiconductor device duringswitching.

With a smoothing circuit, it is generally provided on the input side ofa three-phase inverter or other main switching circuit to controlvariations in voltage.

Inductance in a snubber circuit must he kept very low in order to reducesurge voltage. However, in high-capacity apparatus using high levels ofcurrent and voltage, increased capacitor size and length of wiring meanthat it is difficult to reduce inductance.

Film capacitors (oil type or dry type) are in frequent use, and there isa limit to the extent to which they can be made more compact andinductance reduced.

In the case of smoothing circuits, film capacitors are used for highvoltages, while electrolytic capacitors are used where the main circuitvoltage is less than about 3 kV. The volume and lengthy wiring of theelectrolytic capacitors used for medium and low voltages in particularmake it difficult to reduce inductance, and increase the externaldimensions of the equipment in which they are used.

Meanwhile, ceramic capacitors offer high permittivity and compact size.Moreover, the fact that they are sintered bodies gives them a freedom ofstructure, it is easy to achieve low inductance, and the inorganicnature of the material makes them non-combustible and stable. It alsomeans that in order to achieve high capacity it is necessary to have aserial or parallel structure of unit capacities.

Recent advances have led to the realization of 1 kV/1 μF capacitors foruse in snubber circuits and 600 V/10-1001 μF devices for use insmoothing circuits. Consequently, there is a demand for mountingstructures which allow unit capacitors of this sort to be connected inserial or parallel fashion compactly and with low inductance.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a novelmounting structure for capacitors which permits of high capacity in acompact form achieved by connected ceramic unit capacitors in serial orparallel fashion compactly and with low inductance.

With a view to fulfilling this object, the present invention is amounting structure for capacitors having a plurality of unit capacitorscomprising ceramic capacitor devices with pairs of positive and negativeterminals, and a three-tier (layer) substrate comprising an insulatinglayer sandwiched between two electrodes, wherein a plurality ofapertures is formed in the first electrode, in which are positionedbosses being continuous with the second electrode, while the pluralityof unit capacitors are arranged on the first electrode, one terminal ofeach unit capacitor being in contact with the first electrode and theother with the second electrode via a boss so as to connect all the unitcapacitors electrically in parallel fashion.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a side view of a unit capacitor illustrating an embodiment ofthe present invention;

FIG. 2 is a cross-sectional view illustrating the mounting structure ofthat unit capacitor;

FIG. 3 is a cross-sectional view of the mounting structure illustratinga second embodiment;

FIG. 4 is a cross-sectional view of the mounting structure illustratinga third embodiment;

FIG. 5 is a snubber circuit diagram illustrating a fourth embodiment ofthe present invention;

FIG. 6 is a cross-sectional view of the mounting structure of thesnubber circuit;

FIG. 7 is a smoothing circuit diagram illustrating a fifth embodiment ofthe present invention;

FIG. 8 is a cross-sectional view of the mounting structure of thesmoothing circuit;

FIG. 9 is a cross-sectional view of the mounting structure illustratinga sixth embodiment; and

FIG. 10 is a cross-sectional view of the mounting structure illustratinga seventh embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views,and more particularly to FIG. 1 thereof, one embodiment of the presentinvention will be described.

FIG. 1 shows a unit capacitor 1, which is manufactured by using aceramic such as barium titanate to sinter a rectangular element 2. Toeither end of the element 2 are joined metallic positive and negativeterminals 3 and 4.

The terminals 3 and 4 are flat in shape, and one end is formed into afoot member 3 a and 4 a for the purpose of connection.

FIG. 2 illustrates a plurality of unit capacitors 1 mounted on asubstrate 10. The substrate 10 comprises a three-tier structure whereinan insulating layer 11 is sandwiched between a first electrode 12 and asecond electrode 13.

On the first electrode 12 is formed a plurality of apertures 15, whichare arranged in the same direction. Meanwhile, bosses 16 are formedintegrally with the second electrode 13 in sections corresponding toeach of the apertures 15. Each of these bosses 16 penetrates theinsulating layer 11 to protrude into the corresponding aperture 15, theupper surfaces of the bosses 16 being retained in the same plane as theupper surface of the first electrode 12.

All the unit capacitors 1 are arranged on the first electrode 12 in thesame direction relative to the apertures 15. The foot members 3 a of thepositive terminals 3 of all the unit capacitors 1 are in contact withthe first electrode 12, while the foot members 4 a of the negativeterminals 4 of all the unit capacitors 1 are in contact with the bosses16 within the corresponding apertures 15. In this manner the positiveterminals 3 of all the unit capacitors 1 are in continuity with eachother via the first electrode 12, while the negative terminals 4 are incontinuity with each other via the bosses 16 and the second electrode13, and are thus connected electrically in parallel fashion.

All the terminals 3 and 4 of the unit capacitors are fixed to the firstelectrode 12 and bosses 16 by soldering or screwing.

In a structure of this sort it is possible to ensure high permittivitybecause the elements 2 of the unit capacitors 1 are ceramic, and toachieve compactness and low inductance because ceramic blocks are usedas they are without any cases.

Moreover, because the structure is such that the first terminals 3 ofall the unit capacitors 1 are fixed in contact with the first electrode12 of the three-tier substrate 10 while the second terminals 4 are fixedin contact with the bosses 16 which are in continuity with the secondelectrode 13 so that all the unit capacitors 1 are connected in parallelfashion, it is possible to ensure low inductance of the wiring, and tochange the capacity by increasing or decreasing the number of parallelunit capacitors 1.

The terminals 3 and 4 of the unit capacitors 1 are fixed to the firstelectrode 12 and bosses 16 by soldering or screwing. Soldering enablesthem to be surface-mounted, thus simplifying the manufacturing process,whereas screwing enhances their mechanical strength and resistance toheat cycles.

FIG. 3 illustrates a second embodiment. Here a plurality of unitcapacitors is arranged on either side of the three-tier substrate 10,thus connecting them in parallel fashion.

In other words, a plurality of unit capacitors 1 is arranged on thefirst electrode 12 of the substrate 10 as in the first embodiment. Aplurality of apertures 15 a arranged in the same direction is formed inthe second electrode 13 on the lower side of the substrate 10, and aplurality of bosses 16 a is formed integrally with the first electrode12 in sections corresponding to each of the apertures 15 a. Each ofthese bosses 16 a penetrates the insulating layer 11 to protrude intothe corresponding aperture 15 a.

The foot members 3 a of the positive terminals 3 of all the unitcapacitors 1 on the lower side of the substrate 10 are fixed in contactwith the bosses 16 a, while the foot members 4 a of the negativeterminals 4 are in contact with the second electrode 13. In this mannerall the unit capacitors 1 on both sides of the substrate 10 areconnected electrically in serial fashion.

In this case also the same effect can be achieved as with the firstembodiment, but in comparison with where the unit capacitors 10 arearranged on only one side of the electrode 10 it is possible inparticular to increase their number and double the capacity. On theother hand, if the number of unit capacitors is kept the same, it ispossible to halve the mounting area.

FIG. 4 illustrates a third embodiment. In this embodiment, the firstelectrode 12 and second electrode 13 of the three-tier substrate 10 arein continuity with each other at one end, and the first electrode 12 isdivided into a plurality of independent electrode zones 12 a by means ofa barrier 11 a formed integrally with the insulating layer 11.

A plurality of unit capacitors 1 arranged in the same direction isprovided on the first electrode 12 of the substrate 10. These unitcapacitors are arranged so as to straddle the barriers 11 a insuccession, one terminal 3 being fixed in contact with the neighbouringelectrode zone 12 a from which it is divided by a barrier 11 a while theother terminal 4 is fixed in contact with the other electrode zone 12 a.In this manner all the unit capacitors 1 are connected electrically inserial fashion.

In a structure of this sort it is possible to achieve low inductance andcompactness. It is also possible to set capacitor withstand voltageaccording to the thickness of the insulating layer and the number ofserial unit capacitors 1.

By dividing the second electrode on the lower side of the substrate 10into a plurality of capacitor zones also and fitting a plurality of unitcapacitors there it is possible even with this serial connection toachieve a structure with enhanced capacity and withstand voltage.

FIGS. 5 and 6 illustrate a fourth embodiment, FIG. 5 being a snubbercircuit and FIG. 6 the mounting structure thereof. This snubber circuitcomprises a semiconductor device 21 which acts as a switching element,and a diode 22. A unit capacitor 1 and diode 22 are connected seriallybetween the collector and emitter of the semiconductor device 21.

As may be seen from FIG. 6, the substrate 10 has an electrode 12 on topof an insulating layer 11, the unit capacitor 1 being positioned on theelectrode 12 and comprising a ceramic element 2 with terminals 3 and 4joined on either side.

To the electrode 12 of the substrate 10 in the vicinity of the unitcapacitor 1 is attached a diode 22 by direct soldering using a lowthermal expansion spacer 23 of molybdenum or a similar material. Inother words, a small unit capacitor is provided in the vicinity of thediode in line with the pressure resistance of the device. The unitcapacitor 1 is in continuity with the emitter of the semiconductordevice 21 via the wiring 24, and the diode 22 with the collector of thesemiconductor device 21 via the wiring 25 to form a structure wherein itis possible to suppress surge voltage in the semiconductor device 21during switching (current change×circuit inductance).

The above structure permits of a compact snubber circuit with lowinductance.

FIGS. 7 and 8 illustrate a fifth embodiment, FIG. 7 being a smoothingcircuit and FIG. 8 the mounting structure thereof. This smoothingcircuit comprises a pair of upper and lower switching elements 27, 28and unit capacitor 1.

The unit capacitor 1 is attached to the top of the electrode 12 of thesubstrate 10, and the upper and lower switching devices 27, 28 areattached directly to the electrode 12 in the vicinity of the unitcapacitor 1 by soldering. A heat sink 29 is attached to each of theswitching devices 27 and 28.

The structure is such that the electrode 12 of the substrate 10 isdivided by means of a barrier 11 a into an electrode zone 12 acomprising a unit capacitor 1 and the upper switching device 27, and anelectrode zone 12 b comprising the lower switching device 28. The upperswitching device 27 is in continuity with the lower switching device 28via wiring 30 and with the unit capacitor 1 via the electrode zone 12 a,while the lower switching device 28 is in continuity with the unitcapacitor 1 via wiring 31.

The above structure permits of a compact smoothing circuit with lowinductance.

FIG. 9 illustrates a sixth embodiment in which the ceramic devices 2 ofthe unit capacitors 1 are flat, having positive and negative terminals 3and 4 respectively attached at either side and extending horizontally.

A plurality of unit capacitors 1 of this sort is stacked on top of oneanother, each of the respective positive terminals 3 and negativeterminals 4 in the unit capacitors which face one another as a result ofsuch stacking being joined electrically and mechanically by means ofelectrically conductive spacers 35 so that all the unit capacitors 1 areconnected electrically in serial fashion.

The above structure makes it possible to obtain compact capacitorswithout the need to use wiring, the capacity being dependent on thenumber of unit capacitors 1.

FIG. 10 illustrates a seventh embodiment in which again the ceramicdevices 2 of the unit capacitors 1 are flat, having positive andnegative terminals 3 and 4 attached at either side and extendinghorizontally.

A plurality of unit capacitors 1 of this sort is stacked on top of oneanother. In this case the layers of unit capacitors 1 face alternatelyin opposite directions, the positive terminals 3 and negative terminals4 of the unit capacitors facing one another alternately. In thiscondition, the positive and negative terminals 3 and 4 are joined layerby layer electrically and mechanically by means of electricallyconductive spacers, while the negative and positive terminals 4, 3 arejoined by means of insulating spacers so that all the unit capacitors 1are connected electrically in serial fashion.

The above structure makes it possible to obtain compact capacitorswithout the need to use wiring, the capacity being dependent on thenumber of unit capacitors 1.

As will be clear from the above, the embodiments of the presentinvention facilitate the provision of a compact mounting structure byconnecting ceramic unit capacitors with low inductance in a serial orparallel fashion.

Obviously, numerous additional modifications and variations of thepresent invention are possible in light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe present invention may be practised otherwise than as specificallydescribed herein.

What is claimed is:
 1. A mounting structure for capacitors having aplurality of unit capacitors, comprising: ceramic capacitor devices withpairs of positive and negative terminals; and a substrate that fits saidceramic capacitor devices on said substrate, wherein terminals havingdifferent respective polarities are stacked facing each other, saidterminals having different respective polarities on either side of eachunit capacitor in each layer being connected layer by layer alternatelyby electrically conductive spacers and insulating spacers so as toconnect each of said unit capacitors electrically in serial fashion.